1. Technological Field of the Invention
This invention relates to a room temperature curing silicone elastomer composition, and, in detail, it relates to a composition that becomes a silicone elastomer of low modulus and high elongation after curing at room temperature.
2. Background Information
Compositions that cure at room temperature to form silicone elastomers (room temperature curing silicone elastomer compositions) are known conventionally and are widely used in the industrial world. Known mechanisms of curing this type of composition at room temperature include a mechanism whereby curing is effected by a hydrosilylation reaction, a mechanism whereby curing is effected by ultraviolet rays and a mechanism whereby curing is effected by a condensation reaction of silanol groups and silicon bonded functional groups. Of these, silicone elastomer compositions that are cured by mechanisms by condensation reactions exhibit the characteristics that they can readily exhibit adhesiveness at room temperature, that curing is not readily inhibited by impurities that cure at room temperature, that curing can occur in a short time simply by mixing the principal component and a curing agent, that they can be stored stably for long periods and that they can be cured by allowing them to stand in the atmosphere. They have been widely used for adhesives, coatings, and sealants. However, there is the limitation that workability before curing in respect to mixing, pouring and finishing by manual operation must be maintained, for which reason there has been the problem that mechanical properties are limited. Specifically, it is necessary for the molecular weight of the diorganopolysiloxane, which is the principal component, to be controlled below a certain level in order to facilitate workability. Because of this restriction, it is difficult to keep hardness and modulus of the silicone elastomer after curing below a certain level. For this reason, methods have been proposed in which a polyfunctional cross-linking agent and a bifunctional chain extending agent are used in combination and in which crosslinking and curing are completed as the diorganopolysiloxane chain is being extended (chain extension) during the curing reaction.
Specifically, two methods have been proposed, a method in which a siloxane having two N,N-dialkylaminoxy groups in 1 molecule and a siloxane having three N,N-dialkylaminoxy groups in 1 molecule are used in combination and a method in which a silane having two N-alkylacetamide groups in 1 molecule and a silane having three N-alkylacetamide groups in 1 molecule are used in combination. However, there have been problems with these methods. In the first proposal, i.e., in the method in which N,N-dialkylaminoxy groups are used, N,N-dialkylhydroxylamine is produced as a by-product during the curing reaction. The unpleasant odor of this hydroxylamine has been a problem. Further, hydroxylamine has strong basicity. When atmospheric temperature is slightly increased, siloxane bonds of the diorganopolysiloxane are cleaved, for which reason there has been the major problem that curing is impeded. Siloxanes having N,N-dialkylaminoxy groups are expensive and this is disadvantageous economically. In the method in which N-alkylacetamide groups are used, which is the second proposal, the unpleasant odor of the N-alkylacetamide has been a problem during curing. Moreover, when compounds having active hydrogens such as alcohol are present in the atmosphere, the N-alkylacetamide groups undergo a substitution reaction with the alkoxy groups. As a result, there has been the problem that curing is impeded. In addition, silanes having N-alkylacetamide groups are expensive and are therefore disadvantageous economically. It has also been proposed that chain extension and crosslinking be performed using functional groups that have been widely used conventionally and that do not cause secondary reactions without the use of special, expensive functional groups as seen in the foregoing two proposals. For example, in Japanese Patent Application Kokai No. Sho 63-83167 (1988), a method has been proposed in which HRNCH.sub.2 Si(Me)(OMe).sub.2 (where Me is methyl) is used as the chain extending agent. However, there are the problems that this chain extending agent is difficult to manufacture economically and that it is difficult to achieve a stable balance with the crosslinking agent.
A method using Ph{(Me).sub.3 SiO}Si(OMe).sub.2 (where Ph is phenyl) is proposed in U.S. Pat. No. 4,687,829, issued Aug. 18, 1987, to Chaffee et al. However, initial properties like those when N,N- dialkylaminoxy groups are used cannot be obtained. It is further desirable that the durability properties of silicone construction sealants for use as weather seals meet the standards of construction sealants durability tests 10030 and 9030 as stipulated in JIS A 5758. However, at present, the only construction sealants on the market that satisfy these tests are sealants using silanes that have N,N-dialkylaminoxy groups and sealants that have N-alkylacetamide groups as described above. Sealing materials in which silanes having other functional groups are used do not satisfy these standards.